SU428601A3 - METHOD OF OBTAINING INDOL - Google Patents

Description

This invention relates to a novel process for the production of indole, which is widely used in organic synthesis. A known method for producing indole by dehydrating o-ethylaniline in the presence of titanium dioxide as a catalyst. The object of the present invention is to increase the selectivity of the process. The proposed new method of producing indole is that o-ethylaniline is oxidized by nitrobenzene in the vapor phase at high temperature in the presence of a silica-based catalyst in an inert solvent medium. The catalyst consists of silicon dioxide or contains in its composition various silicon materials with a developed surface, for example, cellite. The catalyst used in combination with an inert solvent reduces the amount of by-products formed. The contact time of the vapor-phase mixture of reagents with the contact catalyst is selected in the range of 0.1-20 seconds, with the optimal duration of contact interaction being 1-10 seconds. The time of contact between the reactants and the catalyst should be understood as the ratio between the volume of the catalyst bed and the volume of the flow of reagents that are in the reaction conditions in the vapor (gaseous) phase. The process can be carried out at temperatures of 300-700 ° C, the optimum temperature is 450-600 ° C. The pressure at which the reaction takes place can be varied within wide limits, and it is not the determining (critical) parameter during the process. It is best to conduct the reaction at atmospheric pressure. A positive factor in carrying out this reaction is the use of a diluent that is inert with respect to the reactants and the catalyst. An example of such inert diluents may be water, nitrogen, argon, carbon dioxide, saturated hydrocarbons, and from the point of view of the optimal mode of the patented process, the use of water is preferable, the molar ratio of which to amine in the reaction mixture may vary from 5: 1 - 50 : 1. The molar ratio between o-ethylaniline and nitrobenzene can vary in the range of 0.2: 1 - 10: 1, the preferred range is 0.5: 1 - 5: 1. In the examples given below, the terms “conversion (degree of conversion) and“ selectivity (degree of selectivity) mean: Amount of reacted Degree of substance (moth) 100 conversion Number of loaded substance (moth). Amount obtained Degree of product (lyuli) 100 selectivity: Amount of reacted substance (moth). Example 1. o-Etr lanillin is oxidized to the pndol using nitrobenzene. An apparatus with an internal diameter of 2.24 cm and a height of 1.3 m is used for the reaction. The reactions are carried out at a temperature of 565-570 ° C and atmospheric pressure. Contact time 5 sec. The molar ratio of o-ethylaniline: nitrobenzene is 3: 2. The inert diluent of the reaction mixture is nitrogen gas. The molar ratio of nitrogen-ethylaniline is 10: 1. In tab. 1 shows the comparative data obtained using two different contact catalysts: Raschiga rings made of ceramic material (experiment A) and silica gel “Lyudoks N. S., extruded in the form of small cylindrical granules of 7X8 mm in size and burned at 500 ° С (experiment B ). Table I The table shows the advantages of using silica gel as a contact catalyst. Example 2. O-Ethylaniline is oxidized to indole when using as an oxide, it is nitrobenzene. The oxidation is carried out in a reactor with an inner diameter of 2.24 cm and a height of 1.3 m. The following were used: contact catalyst: silica gel "Lyudoks N. S., extruded in the form of cylindrical granules 7X8 mm in size and calcined at 500 ° C. Height the catalyst bed in the reactor is 1.20 m. The volume of the catalyst bed in the reactor is 465 cm. The average temperature in the oxidation process is 565-575 ° C. The pressure in the oxidation process is atmospheric. The contact time of the reactants with the catalyst is 5 seconds. The molar ratio of o-ethylaniline: nitrobenzene is 3: 2. In tab. Table 2 shows the results of the oxidation of o-ethylaniline with nitrobenzene. In the conditions described above, in the presence and absence of a diluent. Table 2 The advantages of using an inert diluent when carrying out the oxidation process are so obvious that they do not require additional explanations. Example 3. o-Ethylaniline is oxidized with nitrobenzene to indole in the vapor phase in a reactor with an internal diameter of 3.8 cm. Contact catalyst: Celite in the form of cylindrical granules 4 × 4 mm in size. The height of the catalyst bed in the reactor is 0.55 m. The volume of the catalyst bed in the reactor is 600 cm. The average temperature during the reaction is 570 ° C. The pressure during the reaction is atmospheric. The contact time of the reactants with the catalyst is 4 seconds. The molar ratio of o-ethylamine: nitrobenzene 2: 1. The molar ratio of diluent to o-ethylaniline is 20: 1. In tab. Table 3 shows the data obtained when comparing the results of applying various inert diluents: Table 3

As can be seen from the table, the advantages of using water as an inert diluent are indisputable.

Example 4. O-ethylaniline is acidified with nitrobenzene in the vapor phase to indole in a reactor with an internal diameter of 3.8 cm. A contact catalyst — celite in the form of cylindrical granules 4 × 4 mm in size is used for the reaction. The height of the catalyst bed in the reactor is 0.55 m. The volume of the catalyst bed

600 cm. The reaction is carried out at atmospheric pressure. Thinner: water. The molar ratio of diluent to the mixture of o-ethylaniline and - nitrobenzene is 10: 1.

In tab. Figure 4 shows the data obtained as a result of the process being oxidized at different times of contacting the reactants with the catalyst and at a different molar ratio of o-ethnyl-aryl to nitrobenzene in the reaction mixture.

Example 5. In this example, o-ethylaniline is reacted with o-nitroethylbenzene in a reactor with an internal diameter of 3.8 cm in diameter, a heavy-duty catalyst, which is celite with a grain size of 4x4 mm. The exit of the catalyst bed in the reactor is 0.55 m; volume 600 cm The average reaction temperature is 535 ° C, the pressure is atmospheric. The contact time of the mixture reacts, their suspension with the catalyst is 2.7 seconds. The molar ratio in the reaction mixture is o-ethylaniline: o-nitroethylbenzene 1; the molar ratio of water used as the inert diluent to the starting o-ethylaniline is 15: 1.

Table 4 The rate at which the reactants enter the reaction zone: o-Ethylaniline45 g / hour o-Nitroethylbenzene 56 g / hour The content of o-ethylaniline in the reaction mixture withdrawn from the reactor is 31 g / hour. The yield of the reaction products: indole - 6.1 g / hour, o-aminostyrene - 6.8 g / hour. Object of the invention 1. A method for producing an indole from o-ethylaniline, characterized in that, in order to increase the selectivity of the process, o-ethylaniline is oxidized by nitrobenzene in the vapor phase when heated in the presence of a silica based catalyst in an inert solvent. 2. A method according to claim 1, characterized in that the process is carried out at 450-600 ° C.